Common faults of hydraulic system
There are three basic ‘disease-causing’ factors in hydraulic systems: contamination, overheating and air ingress.
Contamination
The sources of dirt (such as dust, sand, soil, etc.) entering the oil are:
1. The outside of the hydraulic system is not clean. Dirt is brought into the system when refueling or checking the oil level, or enters the system through damaged oil seals or sealing rings.
2. The internal cleaning is not thorough. There are still traces of dirt residues in the oil tank or components.
3. Dirty refueling containers or utensils.
4. Rust is generated inside the pipe due to hot bending of the oil pipe during manufacturing.
5. The oil is not stored properly and is unclean or has deteriorated before being added to the system.
6. Oil that has gradually deteriorated can corrode parts. The corroded metal may become free molecules suspended in the oil.
Dirt can cause wear and corrosion of parts, especially for precision-machined parts. They will scratch the inner wall of the rubber tube, the oil seal ring and the packing, and the damage of these things will cause more dirt to enter the system, thus forming a vicious cycle of damage.
Overheating
System overheating may be caused by one or more of the following reasons:
1. Air or moisture enters the oil. When the hydraulic pump converts the oil into pressure oil, the air and moisture will contribute to the increase of heat and cause overheating.
2. The oil level in the container is too high, and the oil is stirred violently, causing overheating.
3. Poor quality oil may be thinner, allowing foreign matter to remain in suspension, or have an affinity for water, which can also cause heat generation.
4. When working beyond the rated working capacity, heat is generated.
5. Improper adjustment of the oil return valve or failure to replace damaged parts in time can sometimes cause heat.
Overheating will cause the oil to oxidize rapidly, which in turn will release insoluble resins, sludge and acids. These substances accumulate in the oil, causing accelerated wear and corrosion of parts, and they adhere to the surface of the finished parts, causing the parts to lose their original function. The oil becomes thinner due to overheating, which will also cause the transmission to work slowly.
The above-mentioned overheating results in slow transmission and stuck oil return valve during operation.
Air ingress
There are several reasons why air enters the oil:
1. Improper pouring downwards during refueling causes bubbles to mix into the oil and be carried into the pipeline.
2. The joint is loose or the oil seal is damaged, and air is sucked in.
3. The oil suction line is worn, scratched or corroded, allowing air to enter.
In addition to causing overheating, a considerable amount of air will be dissolved in the oil under pressure. If about 10% of the compressed volume is dissolved air, foam will form when the pressure drops. When the working hydraulic cylinder reduces pressure and returns oil, the foamy oil will form a "sponge" property. In addition, oil containing a lot of foam will increase the total volume and cause the oil tank or reservoir to overflow.
Working oil containing air will produce sudden spasms when transmitting power, making the power transmission uneven. The resulting pressure fluctuations and stress will damage components and, in severe cases, the entire system.
Working oil containing air can also create the risk of cavitation in the hydraulic pump, which creates a greater suction force and draws more air into the system along with other impurities. Overheating occurs due to the entry of air into the oil, and dust is brought in with the air, which can cause the oil to deteriorate quickly.
Maintenance method
1. Check all piping systems for flattening, bending and damage, and check hoses for kinks, abrasions or excessive bends.
2. To prevent any tiny dust and dirt from sticking to the internal parts, steam clean the entire system if possible.
3. Check the fuel tank or reservoir to see if the oil level is sufficient and whether the refueling process causes foaming, agitation or eddy currents. These phenomena are signs of air ingress. The appearance of foam at the vent indicates that air has entered.
4. Check whether the pipes and other components have peeled paint due to overheating, whether there is a burning smell, and whether the oil has become black and thick. Measuring oil temperature with a thermometer.
5. Check for leaks by applying soap foam to the joints. There may be oil stains where there are leaks, because oil will absorb dirt, but the presence of oil stains does not necessarily mean there are leaks. In addition, overheating often indicates leakage. If any leaking joints are found, tighten them immediately.
6. Listen for any abnormal noises. If the hydraulic pump makes a ‘clicking’ sound, it may be due to air entering and causing cavitation, or it may be worn out by dirt.
7. Regularly check the working capacity of the hydraulic pump.